J. Balderston

MEASUREMENT OF THE TOP QUARK PAIR PRODUCTION CROSS SECTION IN PP COLLISIONS

We present a measurement of the ttbar production cross section in ppbar collisions at root(s) = 1.8TeV by the D0 experiment at the Fermilab Tevatron. The measurement is based on data from an integrated luminosity of approximately 125 pb^-1 accumulated during the 1992-1996 collider run. We observe 39 ttbar candidate events in the dilepton and lepton+jets decay channels with an expected background of 13.7+-2.2 events. For a top quark mass of 173.3GeV/c^2, we measure the ttbar production cross section to be 5.5+-1.8 pb.

Search for the decay b→Xsμ+μ−

Abstract We have searched for the flavor-changing neutral current decay b → X s μ + μ − in p p collisions at s = 1.8 TeV with the DO detector at Fermilab. We determine the 90% confidence level limit for the branching fraction to be B ( b → X s μ + μ − ) −4 . We argue that this limit is more stringent than the best published limit on this decay rate.We have searched for the flavor-changing neutral current decay b ->s mu+ mu- in p pbar collisions at sqrt(s) = 1.8 TeV with the DO detector at Fermilab. We determine the 90% confidence level limit for the branching fraction to be B(b ->X_s mu+ mu-)<3.2 x 10^{-4}. We argue that this limit is more stringent than the best published limit on this decay rate.

Second generation leptoquark search in pp-bar collisions at sqrt s=1.8 TeV.

We report on a search for second generation scalar leptoquarks with the D0 detector at the Fermilab Tevatron {ital pp}{ovr bar} collider at {radical}{ital s}=1.8TeV. This search is based on 12.7pb{sup {minus}1} of data. Second generation leptoquarks are assumed to be produced in pairs and to decay into a muon and quark with branching ratio {beta} or into a neutrino and quark with branching ratio 1{minus}{beta}. We obtain cross section times branching ratio limits as a function of leptoquark mass and set lower limits on the leptoquark mass at the 95% confidence level. {copyright} {ital 1995} {ital The} {ital American} {ital Physical} {ital Society}.

Search for diphoton events with large missing transverse energy in

A search for signals of new physics has been carried out in the channel p pbar -> gamma gamma + ETmiss. This signature is expected in various recently proposed supersymmetric (SUSY) models. We observe 842 events with two photons having transverse momentum ET(g) > 12 GeV and pseudorapidity |eta(g)| gamma gamma ETmiss + X) where ET(g) > 12 GeV, |eta(g)| 25 GeV.

pp

The results of a search for W boson pair production in pp collisions at √s=1.8TeV with subsequent decay to eμ, ee, and μμ channels are presented. Five candidate events are observed with an expected background of 3.1±0.4 events for an integrated luminosity of approximately 97pb -1 . Limits on the anomalous couplings are obtained from a maximum likelihood fit of the E T spectra of the leptons in the candidate events. Assuming identical WWγ and WWZ couplings, the 95% C.L. limits are -0.62<Δκ<0.77 (λ=0) and -0.53<λ<0.56 (Δκ=0) for a form factor scale Λ=1.5TeV.

collisions at

Limits on the anomalous WWγ and WWZ couplings are presented from a simultaneous fit to the data samples of three gauge boson pair final states in pp collisions at √s=1.8TeV: Wγ production with the W boson decaying to eν or μν, W boson pair production with both of the W bosons decaying to eν or μν, and WW or WZ production with one W boson decaying to eν and the other W boson or the Z boson decaying to two jets. Assuming identical WWγ and WWZ couplings, 95% C.L. limits on the anomalous couplings of -0.30<Δκ<0.43 (λ=0) and -0.20<λ<0.20 (Δκ=0) are obtained using a form factor scale Λ=2.0TeV. Limits found under other assumptions on the relationship between the WWγ and WWZ couplings are also presented.

s = 1.8

We report on a search for right-handed

TeV

W

Limits on [Formula Presented] and [Formula Presented] couplings from [Formula Presented] boson pair production

bosons (

Limits on anomalous [Formula Presented] and [Formula Presented] couplings

W_R